Power transmission



p 1966 J. v. BLOOMQUIST 3,272,135

POWER TRANSMISSION Filed April 5, 1963 INVENTOR.

JAMES v. BLOOMQUIST BY% flulu. M

ATTORNEYS United States Patent 3,272,135 POWER TRANSMISSION James V. Bloomquist, Madison Heights, Micl1., assignor to Sperry Rand Corporation, Troy, Mich, a corporation of Delaware Filed Apr. 5, 1963, Ser. No. 270,945 6 Claims. (Cl. 10338) This invention relates to power transmissions, and more particularly to those of the type comprising two or more fluid pressure energy translating devices, one of which may function as a pump and another as a fluid motor.

The invention particularly relates to such a transmission employing a pressure compensated variable displacement pump, the pump displacement being reduced in response to an increase in outlet pressure.

The conventional pressure compensating control includes a simple pilot valve having a pressure effective area on which pump outlet pressure is imposed to act in opposition to a biasing spring, the force of which spring establishes the point at which pump displacement reduction begins. Such a conventional control is shown in US. Patent No. 2,834,297 to Postel et al., FIGURE 9. Since the conventional compensator employs only proportional feedback of pump outlet pressure, stability of control is not adequate for more demanding applications.

It is, therefore, an object of the present invention to provide an improved control for a pressure compensated pump, in which overshoot and transient fluctuations in pump displacement and outlet pressure are minimized.

It is a further object of this invention to provide such a control having improved stability Without impairment of response time and without appreciable increase in size and weight as compared to the conventional compensator.

Further objects and advantages of the present invention will be apparent from the following description, reference being bad to the accompanying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing:

The single figure is a diagrammatic view of a power transmission system incorporating a preferred form of the present invention.

Referring now to the drawing, the hydraulic transmission comprises a variable displacement pump 10 having its outlet connected through a pressure conduit 12 to a control valve 14 and a fluid motor 16 driving a load 18. Exhaust fluid from motor 16 is returned to a reservoir 20 through a low pressure conduit 22. The inlet of pump 10 is supplied with fluid from reservoir 20 through a conduit 24.

Pump it is of the well-known swinging yoke type which is shown in detail in the aforementioned Postel, et al. patent and is therefore merely schematically represented in the drawing. The displacement of pump 10 is varied by varying the position of yoke 26. With yoke 26 in the position shown, pump displacement will be at its maximum. Swinging yoke 26 in the direction of arrow 28 will reduce pump displacement.

An actuator 30 is provided for the yoke 26 and comprises a control piston 32 connected to yoke 26 by linkage 34, piston 32 being biased by a spring 36 so as to induce maximum pump displacement. It will be seen that pressure in chamber 38 will act on piston 32 in opposition to spring 36 and induce reduced pump displacement.

The pressure compensating control valve generally designated 40 includes a body 42 having three ports 44, 46 and 48 therein. These ports are connected respectively by lines 50, 52 and 54 to the pump outlet, the control piston chamber 38 and reservoir 20. Lines 50, 52 and 54- schematically indicate connections which would normally be effected by passages within the pump housing 3,Z7Z,l35 Patented Sept. 13, 1966 terminating in a mounting pad upon which valve body 42 would be mounted, in the same manner as shown in FIGURE 9 of Postel et. al.

The body 42 of valve 40 includes a central bore 56 closed at one end by a plug 58 and at the other by a cover 60. A sleeve 62 is inserted in bore 56 and contains a valve bore 64 in which a valve spool 66 is slidably inserted. Spool 66 carries a first land 68 which controls communication between ports 44 and 46, and a second land 76 which controls communication between ports 46 and 48.

A bore 72 extends through the end of sleeve 62 and slidably receives a sensing spool 74 which projects into chamber 76. Chamber 76 is formed in part by the bore 56 and in part by a cavity 78 in the plug 58. Sensing spool 74 has a smaller diameter than valve spool 66. A spring 80 normally urges the sensing spool 74 into abutment with the valve spool 66 which in turn abuts stop 82 on cover 60. In the normal, spring biased position of valve spool 66, the land 68 isolates port 44 from port 46, while the land '70 permits communication between ports 46 and 48. The biasing force imposed by spring 80 can be adjusted through the support rod 84, and the volume of chamber 76 can be adjusted by threading the plug 58 further into or out of body 42. If even greater volume is desired for chamber 76, a plug similar to plug 58 but having a larger cavity 78 can be substituted.

Sleeve 62 includes a drilled passage 86 extending in an axial direction from end to end, in which is inserted a plug 88 having a sharp-edged orifice 90 therein. Prior to operation of the system, the chamber 76 is filled with the same hydraulic fluid used in the pumping system, which fluid will have a bulk modulus (E) which may be expressed in terms of pounds per square inch.

The volume of chamber 76 may be expressed in terms of cubic inches and is hereinafter referred to as V The right-hand-end projected area of spool 66, which is exposed to pump outlet pressure, may be expressed in square inches and is hereinafter referred to as A The projected area of sensing spool 74 exposed to pressure in a chamber 76 may be expressed in square inches will be referred to as A The rate of spring 60 expressed in pounds per inch will be referred to as K It will be seen that with a slowly increasing pump outlet pressure a point will be reached at which outlet pressure acting on area A will overcome the force of spring 80 plus pressure in chamber 76 acting on the smaller A causing spool 66 to shift so that land 68 will permit communication between ports 44 and 46, thus porting high pressure fluid to the chamber 38 to cause reduction in displacement of pump 10. In the case of a slow increase or decrease in pump outlet pressure the restrictive effect of orifice 90 and the compressibility of the volume of [fluid V will not be significant factors and operation of the control will be very similar to a standard compensating control of the type shown in Postel, et. al., in which the effective feedback is proportional only to pump outlet pressure.

However, in the case of step changes in pump outlet pressure or high frequency signal modulation from the control valve =14 the conventional pressure compensator induces overshoot and a gradually decaying hunting condition lbefore stabilization is finally achieved. In systems demanding a high degree of compliance and rapid response the standard compensator has been found inadequate. The present invention provides greatly increased stability and reduces both pressure overshoot and response time by producing a leading feedback relative to pump outlet pressure at oscillation frequencies. The lead circuit comprises the compressible volume V sensing spool area A and orifice 90.

The formula:

ID li Ali a 1 .vo

is a dimensionless measure of the leading phase angle of feedback (qb) to be obtained from a given set of parameters. It has been found that a :1: of approximately 2.0 is sutficient to provide adequate stabilization for most applications. However, values in the range of 1.5 to 5.0 have been employed eifectively in particular circuits. A large not only increases the maximum obtainable leading phase angle, but the leading phase angle is provided over a larger frequency range. It will be seen that a fine adjustment of 4) can be obtained by threading plug 68 farther in or out of the body 42 and thus varying the quantity V In a particular compensator, components and a fluid having the following parameters were employed.

resulting in a value of 2.21.

V volumes in the range from .75 to 3.0 cubic inches have been found to be effective and are recommended although it should be noted that it is the relation between the various parameters that is of primary importance, rather than the absolute value of any one parameter.

The optimum diameter of orifice 90 is to some extent a function of particular pump characteristics, and the volume of working oil under compression in communication with the pump outlet. This volume will vary in different applications and the proper orifice size may best be determined by experimentation. In general, the larger the volume under compression, the smaller the orifice size.

In testing the particular compensator whose parameters are set forth above, it was found that sizes of orifice 90 in the range from .010 to .050 inch in diameter were effective. On a specific pump, an orifice of .0125 inch in diameter was optimum for a volume of cubic inches under compression. On the same pump, an orifice of .010 inch in diameter was optimum for 80 and more cubic inches under compression. On another pump, an orifice diameter of .015 inch was optimum for 80 cubic inches under compression and .010 inch was optimum for 300 and more cubic inches under compression.

Pressure compensators incorporating the present invention have been directly substituted for conventional pressure compensators in a number of hydraulic systems with remarkable improvements in compliance and in response and stabilization times. It will thus be seen that the present invention has provided an improved pressure compensating control for variable displacement pumps.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a hydraulic power transmission employing a variable displacement pump having an outlet connected by a pressure conduit to a load, and actuator means for varying the displacement of said pump, control means for said actuator comprising: shiftable valve means for directing fluid to said actuator; resilient means biasing said valve means in one direction; means forming a first area associated with said valve means and exposed to pressure from the outlet of said pump so as to urge said valve in a direction opposite to said one direction; means forming a second area, smaller than said first area, associated with said valve means so as to urge said valve in said one direction in response to pressure thereon; means forming an enclosed chamber, pressure in which is imposed on said second area; continuously open passage means extending between said first area and said chamber and forming the sole means of egress for fluid from said chamber; and a restriction in said passage means.

2. In a hydraulic power transmission employing a variable displacement pump having an outlet connected by a pressure conduit to a load, and actuator means for varying the displacement of said pump, control means for said actuator comprising: shiftable valve means for directing fluid to said actuator; resilient means biasing said valve means in one direction; means forming a first area associated with said valve means and exposed to pressure from the outlet of said pump so as to urge said valve in a direction opposite to said one direction; means forming a second area, smaller than said first area, associated with said valve means so as to urge said valve in said one direction in response to pressure thereon; means forming an enclosed chamber, pressure in which is imposed on said second area; continuously open means for adjusting the size of said chamber; passage means extending between said first area and said chamber and forming the sole means of egress for fluid from said chamber; and a restriction in said passage means.

3. In a hydraulic power transmission employing a variable displacement pump for pumping a fluid having a bulk modulus B and having an outlet connected by a pressure conduit to a load, and actuator means for varying the displacement of said pump, control means for said actuator comprising: shiftable valve means for directing fluid to said actuator; resilient means having a spring rate of K biasing said valve means in one direction; means forming a first area (A.,) associated with said valve means and exposed to pressure from the outlet of said pump so as to urge said valve in a direction opposite to said one direction; means forming a second area (A smaller than said first area, associated with said valve means so as to urge said valve in said one direction in response to pressure thereon; means forming an enclosed chamber having a volume V pressure in which is imposed on said second area; continuously open passage means extending between said first area and said chamber and forming the sole means of egress for fluid from said chamber, the aforementioned parameters being so related that divided by l-I- U is 1.5 or greater; and a restriction in said passage means. 4. In a hydraulic power transmission employing a variable displacement pump for pumping a fluid having a bulk modulus B and having an outlet connected by a pressure conduit to a load, and actuator means for varying the displacement of said pump, control means for said actuator comprising: shiftable valve means for directing fluid to said actuator; resilient means having a spring rate of K biasing said valve means in one direction; means forming a first area (A associated with said valve means and exposed to pressure from the outlet of said pump so as to urge said valve in a direction opposite to said one direction; means forming a second area (A smaller than said first area, associated with said valve means so as to urge said valve in said one direction in response to pressure thereon; means forming an enclosed chamber having a volume V pressure in which is imposed on said second area; continuously open passage means extending between said first area and said chamber and forming the sole means of egress for fluid from said chamber, the aforementioned parameters being so related that c Ak B m; dlvlded by 1+KBVO said restriction comprising a sharp-edged orifice having a diameter in the range from .010 to .050 inch.

5. In a hydraulic power transmission employing a variable displacement pump for pumping a fluid having a bulk modulus B and having an outlet connected by a pressure conduit to a load, and actuator means for varying the displacement of said pump, control means for said actuator comprising: shiftable valve means for directing fluid to said actuator; resilient means having a spring rate of K biasing said valve means in one direction; means forming a first area (A associated with said valve means and exposed to pressure from the outlet of said pump so as to urge said valve in a direction opposite to said one direction; means forming a second area (A smaller than said first area, associated with said valve means so as to urge said valve in said one direction in response to pressure thereon; means forming an enclosed chamber having a volume V in the range from .75 to 3.0 cubic inches, pressure in which is imposed on said second area; continuously open passage means extending between said first area and said chamber and forming the sole means of egress for fluid from said chamber, the aforementioned para-meters being so related that valve means and exposed to pressure from the outlet of said pump so as to urge said valve in a direction opposite to said one direction; means forming a second area (A smaller than said first area, associated with said valve means so as to urge said valve in said one direction in response to pressure thereon; means forming an enclosed chamber having a volume V in the range from .75 to 3.0 cubic inches, pressure in which is imposed on said second area; continuously open passage means extending between said first area and said chamber and forming the sole means of egress for fluid from said chamber, the aforementioned parameters being so related that A B s V0 is 1.5 or greater; and a restriction in said passage means,

said restriction comprising a sharp-edged orifice having a diameter in the range from .010 to .050 inch.

A9 E A; dlvlded by 1 References Cited by the Examiner UNITED STATES PATENTS MARK NEWMAN, Primary Examiner.

DONLEY I. STOCKING, SAMUEL LEVINE,

Examiners. W. L. FREEH, Assistant Examiner. 

1. IN A HYDRAULIC POWER TRANSMISSION EMPLOYING A VARIABLE DISPLACEMENT PUMP HAVING AN OUTLET CONNECTED BY A PRESSURE CONDUIT TO A LOAD, AND ACTUATOR MEANS FOR VARYING THE DISPLACEMENT OF SAID PUMP, CONTROL MEANS FOR SAID ACTUATOR COMPRISING: SHIFTABLE VALVE MEANS FOR DIRECTING FLUID TO SAID ACTUATOR; RESILIENT MEANS BIASING SAID VALVE MEANS IN ONE DIRECTION; MEANS FORMING A FIRST AREA ASSOCIATED WITH SAID VALVE MEANS AND EXPOSED TO PRESSURE FROM THE OUTLET OF SAID PUMP SO AS TO URGE SAID VALVE IN A DIRECTION OPPOSITE TO SAID ONE DIRECTION; MEANS FORMING A SECOND AREA, SMALLER THAN SAID FIRST AREA, ASSOCIATED WITH SAID VALVE MEANS SO AS TO URGE SAID VALVE IN SAID ONE DIRECTION IN RESPONSE TO PRESSURE THEREON; MEANS FORMING AN ENCLOSED CHAMBER, PRESSURE IN WHICH IS IMPOSED ON SAID SECOND AREA; CONTINUOUSLY OPEN PASSAGE MEANS EXTENDING BEWEEN SAID FIRST AREA AND SAID CHAMBER AND FORMING THE SOLE MEANS OF EGRESS FOR FLUID FROM SAID CHAMBER; AND A RESTRICTION IN SAID PASSAGE MEANS. 